Machine gun having a firing system means for obtaining substantially constant and minimum recoil forces

ABSTRACT

A machine gun in which the recoil forces produced during a firing burst are substantially constant and are reduced to a minimum is provided with a cradle, a recoiling mass including a barrel and breech assembly slidingly mounted on the cradle for displacement responsive to discharge forces, a substantially constant accelerating force for driving the recoiling mass forward on the cradle, and a computerized firing system. The firing system comprises sensors providing signals proportional to forward displacement and velocity of the recoiling mass relative to a fixed point on the cradle and the acceleration of the cradle in the direction of fire with a control device comprising a computer and a comparator programmed to fire a round, responsive to signals from the sensors, at a point of time when the forward displacement and velocity of the recoiling mass and the acceleration of the cradle have values such that when a round is fired the impulse imparted to the recoiling mass is sufficient to drive the recoiling mass rearwardly to a reference point where its velocity will be zero.

Unite $3198 ate [151 3,677,135 Hang, Jr. 1 July 18, 1972 MACI'HNE GUN HAVKNG A Primary Examiner-Stephen C. Bentley Edward J. Haug, In, Davenport,'lowa The United States of America as represented bythe oltheArmy Filed: Nov. 19, 1969 Appl. No.: 878,120

Inventor:

Assignee:

US. Cl. ..89/42 B, 89/44, 89/135 Int. Cl.. 4" 19/ 10 Field of Search ..89/42, 42 B, 43, 44, 135

References Cited UNITED STATES PATENTS 3/1971 Williams et al ..89/43 R 3/1911 Haussner ..89/42 B 9/1919 Smith .89/l35 Attorney-Harry M. Saragovitz, Edward J. Kelly, Herbert Berl and Albert E. Arnold, Jr.

[57] ABSTRACT A machine gun in which the recoil forces produced during a firing burst are substantially constant and are reduced to a minimum is provided with a cradle, a recoiling mass including a barrel and breech assembly slidingly mounted on the cradle for displacement responsive to discharge forces, a substantially constant accelerating force for driving the recoiling mass forward on the cradle, and a computerized firing system. The firing system comprises sensors providing signals proportional to forward displacement and velocity of the recoiling mass relative to a fixed point on the cradle and the acceleration of the cradle in the direction of fire with a control device comprising a computer and a comparator programmed to fire a round, responsive to signals from the sensors, at a point of time when the forward displacement and velocity of the recoiling mass and the acceleration of the cradle have values such that when a round is fired the impulse imparted to the recoiling mass is sufiicient to drive the recoiling mass rearwardly to a reference point where its velocity will be zero.

5 Claims, 2 Drawing figures COMPUTER OMPARATOR wimmmemz 3.671.135

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COMPUTER OMPARATOR A L X Ei pi OMPUTER COMPARATOR INVENTOR EELWILTEL J H11u g;JI-.

BY. 7 w g GEM/Wm ATTORNEYS BACKGROUND OF THE INVENTION The U. S. Army has been using guns since its founding and machine guns since about 1900. Machine guns, particularly, have been designed so as to be rugged and reliable in a wide variety of environments. The philosophy applied to machine gun designs in the past has led to an efiective family of weapons for ground use and for mounting on ground vehicles and semi-rigid airplanes. Mounting this family of weapons on helicopters, however, has generated severe problems which require a new philosophy.

In the past, relatively little attention has been given to radically changing the nature of the recoil forces produced by machine gun fire. Most machine guns yield pulsating recoil forces with extremely high peaks applied to the gun mount. This kind of recoil force is particularly detrimental to performance when the gun is mounted on a helicopter because of problems which arise due to the interaction of the gun and the extremely flexible helicopter frame.

One of the difficulties associated with this pulsating recoil force is the design of the supporting structure and the fire control equipment so that they will perform their functions within weight constraints. It is obvious that if the peak recoil forces can be reduced substantially then considerable weight saving can be realized. Further, because of the peak recoil forces the caliber of the weapons mounted on the helicopters have had to be limited. With the reduction of the extremely high peaks of the recoil forces, helicopters could act as airborne artillery.

A much more severe problem is the structural vibration which is excited by the pulsating recoil forces. Amplitudes of angular vibration of up to miliradians are observed when some of the standard machine guns are fired and such oscillations represent aim error which is outside acceptable limits. This vibration environment is also detrimental to equipment located in the neighborhood of the weapon.

SUMMARY OF THE INVENTION The problems generated by these pulsating recoil forces are overcome by this invention in which the recoil forces are reduced to a minimum and are substantially constant during the entire period of fire.

The principal of operation employed is similar to that used in out-of-battery firing of artillery pieces. The cyclic operation and the presence of disturbances in helicopter mounted machine guns, however, require a more sophisticated firing system than is needed in artillery applications. When the invention was adapted to an M39, mm Automatic Gun which, as originally designed, produces peak recoil variation of +2000 lbs. to -2000 lbs., the recoil force was reduced to between 330 and 355 lbs. and was substantially constant when the weapon was fired at 600 rounds per minute.

It is therefore a principal object of this invention to provide a machine gun in which the recoil forces are reduced to a minimum and are substantially constant.

It is a further object of this invention to provide a machine gun having a cradle and a recoiling mass mounted thereon for displacement responsive to recoil forces produced by discharge of rounds therein with a firing system in which a signal is generated to fire a round when the displacement and velocity of the recoiling mass and the acceleration of the cradle in the line of fire have values such that when the firing impulse is applied to the recoiling mass, the recoiling mass is driven rearwardly to a predetermined recoil position where its velocity is zero. That is, the weapon is to operate in a stable mode in spite of external disturbances.

It is still another object of this invention to provide such firing system with sensors mounted on the recoiling mass to provide electrical signals proportional to the forward displacement and the velocity of the recoiling mass relative to a fixed point on the cradle and another sensor mounted to the cradle for signaling the component of acceleration thereof, a computer for evaluating the signals transferred thereto by the sensors and a comparator for monitoring the computer evaluation to fire the round at the desired point of time.

Ftuther objects and advantages of the invention will be apparent from the following specification and the accompanying drawings which are for the purpose of illustration only.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of the machine gun of this invention with the recoiling mass shown at its normal at-rest position; and

FIG. 2 is a view similar to FIG. 1 but showing the recoiling mass at its recoil position.

DESCRIPTION OF THE PREFERRED EMBODIMENT Shown in the figures is a machine gun 12 comprising a cradle 14 provided with a pair of trunnions 15 for mounting the machine gun to a helicopter frame 16, and a recoiling mass 18 including a barrel 19 mounted on the cradle for sliding reciprocal displacement along the line of fire responsive to recoil forces generated when an electrically discharged round is fired into the barrel. An energizing spring 20 is disposed between the rear of mass 18 and the rear end of cradle 14 for resiliently stopping rearward travel of the recoiling mass at a recoil position and accelerating it forwardly. A spring actuated buffer 21 is located at the front end of cradle 14 to provide a forward buffer for recoiling mass 18 and to oppose spring 20 so as to resiliently hold the recoiling mass at a point of equilibrium when a firing burst is completed.

Machine gun 12 is fired by a firing system 22 ,which includes a sensor 24 and a sensor 26 which are mounted to recoiling mass 18 to respectively provide electrical signals proportional to the displacement and the velocity of the recoiling mass, relative to a fixed point on cradle 14, during forward acceleration thereof. An accelerometer 28 is mounted on cradle 14 to sense the component of acceleration thereof with frame 16 along the axis of barrel l9. Sensors 24 and 26 and accelerometer 28 are electrically connected to an analog computer 30 'so as to feed their signals thereinto. Computer 30 is electrically connected to a comparator 32 which compares the input values to those programmed therein and, when the input values go from a plus to a minus, a signal is given to firing circuit 33 which functions to ignite the round which is in position to be fired.

Spring 20 is designed to provide a substantially constant predetermined force P which is applied to the recoiling mass to accelerate it forwardly from its recoil position. Spring buffer 21 is designed to counter spring 20 so as to put recoiling mass 18 into equilibrium at a fixed distance forward of the recoil position when firing ceases. A firing burst is initiated while recoiling mass 18 is at-rest. When the firing burst is initiated with recoiling mass 18 at the at-rest position, the recoiling mass moves rearwardly under the influence of the recoil forces produced by the discharge until it comes to rest at a recoil position, where x 0, with x denoting displacement of the recoiling mass relative to cradle 14. Under the influence of force P, recoiling mass 18 will immediately accelerate forwardly and the round will be fired by firing system 22 at a time which will guarantee that the recoiling mass, responsive to the firing impulse, will move rearwardly and be decelerated by the force P so as to come to rest at the recoil position, x 0.

Cyclic operation depends upon the magnitude of force P and the time at which the round is fired during forward displacement of recoiling mass 18. These quantities are determined based upon the properties of machine gun l2 and the desire performance thereof. If machine gun 12 is to fire R rounds per second, then, neglecting momentum loss due to internal functioning of the weapon, over one cycle of operation (1/R) P= H,, where (HR time of one cycle and H momentum of round and gases leaving the gun barrel of recoiling mass. This equation states the relation between the change in momentum of recoiling mass 18 for one round over one cycle due to the applied force P. Nominally then P= R H Determination of the time when machine gun 12 is to be fired during its operating cycle is more complex because the weapon must be fired when the relationship between displacement and velocity of recoiling mass 18 is such that when a round is fired recoiling mass under the action of force P comes to rest at the recoil position, x 0. Therefore, machine gun 12 must be fired when the velocity of recoiling mass 18 is such that S( v,P) =x, where S( v,P) denotes the distance, as a function of velocity, and force P, the recoiling mass travels to the rear before it comes to rest. The function S( v,P) is a property of machine gun l2 and force P is determined as hereinafter described. Sensors 24 and 26 implement this logic by recording displacement is and velocity v of recoiling mass 18 relative to cradle 14. The quantity S(v,P) is then computed by computer 30 and monitored by comparator 32, as hereinafter described, so that when S( v,P) x changes from positive to negative a signal is transmitted from the comparator to firing circuit 33 to fire the round which is indexed to barrel 19.

The above assumes that frame 16 is perfectly stationary. Any weapon, however, which is mounted on a helicopter must be capable of operating in an extreme environment. Gross motion of frame 16 and variations in the elevation, measured from horizontal, of machine gun 12 must be accounted for since they may have an adverse effect on its functioning. Further, while it is not attributable to the helicopter vehicle, the normal variations in ammunition may cause limited adverse effect.

Both of these disturbances have the effect of causing an error in S( v,P) which means that if they are present and machine gun 12 is fired when S(v,P) x =0, recoiling mass 18 might not move S( v,P) units to the rear in recoil before coming to rest. It would not, therefore, come to rest at the predetermined recoil position. The very nature of the firing system 22, which is self-correcting for disturbances within tolerable limits, allows for corrections of these errors. Computer simulations have verified that this is the case for vibration amplitudes three times as large as those found in most weapons, for 10 percent error in H and for ignition delay of three miliseconds with a weapon firing at a rate of 10 rounds per second.

As to corrections for variations in the acceleration of cradle 14: Gross motion of frame 16 and variations in the elevation of machine gun 12 have the effect of accelerating cradle 14 in an inertial reference frame. Since the coordinate x is measured relative to cradle 14, the acceleration of the cradle, therefore, effectively changes P which in turn causes a change in S( v,P). These changes can be accounted for analytically as follows:

Let 2 be the coordinate of cradle 14 in the direction of fire and measured in an inertial coordinate system. Then Newtons Second Law applied to the recoil-mass 18 is P M a 2), where M,,= mass ofrecoiling mass 18,

d/dt, and

This equation may be rewritten as P M 2 M, 35 Machine gun 12 is then acted on by an effective force F= P M, 2 relative to cradle 14.

As noted hereinbefore, S( v,P) depends on the applied force P. Therefore, with S( v,P) predetermined as hereinafter described, in order to correct for the error due to gross motion and elevation the acceleration of cradle 14, 2', is measured by accelerometer 28 which is attached to cradle 14. Force P is now replaced by the effective force P in S(v,P). The firing algorithm is now taken as:

Each round is fired when the electrical signal Q( ,i) p) as developed by computer 30 and monitored by comparator 32, changes from positive to negative. In this equation, v,x and 'z' are measured respectively by sensors 26 and 24 and accelerometer 28 and the values are transmitted to computer 30 for evaluation by the analog circuits thereof. Once P is determined by the equation of P R H as stated hereinbefore, the function S( v,P) is then determined. It may be determined either through dynamic analysis of machine gun 12 or by experiment.

By the experimental method, for a given force P, recoiling mass 18 is accelerated from the predetermined recoil position where x 0 and fired at several predetermined velocities v The distance recoiling mass 18 recoils before coming to rest is measured and recorded as S(v P). The experiments are repeated for several values of P, say P, This yields a set of values S(v aP which can now be used to form an approximation of S(v,P).

Since electrical power is available on board a helicopter and other vehicles on which machine gun 12 would be mounted, power is provided for computer 30 and comparator 32 from the vehicle. Computer 30 is a simple analog circuit which evaluates Q(v,x,2) of the equation Q(v,x,2) S(v,P M92) x using signals from sensors 24 and 26 and accelerometer 28. Comparator 32 is used to trigger firing circuit 33 when Q changes from positive to negative. Computer 30 and comparator 32 may both be obtained from commercial sources in small packages so that they are readily mounted to machine gun l2 and add little weight and bulk thereto.

Thus, when machine gun 12 is fired from the initial at-rest position, recoiling mass 18 is driven rearwardly by the recoil forces and brought to rest at the recoil position, x 0, due to force P applied by spring 20. Under the influence of force P, recoiling mass 18 is accelerated forwardly with the variable values of factors v,x and 2 being measured by sensors 24 and 26 and accelerometer 28 and transmitted to computer 30 where they are computed according to the control equation stated above and then transmitted to comparator 32 for monitoring. When Q in the value of the control equation Q(v,x,2) S(v,P Mi) x goes from plus to minus, comparator 32 signals firing circuit 33 to fire the round.

During the subsequent discharges in a firing burst, the points at which the discharges occur during the forward displacement of recoiling mass 18 are automatically varied to compensate for any adverse disturbances and therefore with the recoil momentum being opposed by force P a minimum and substantially constant force is applied from recoiling mass 18 to cradle 14 and therefrom to frame 16 and pulsating forces with high peaks are almost completely eliminated.

I wish it to be understood that I do not desire to be limited to the exact details of construction shown and described, for obvious modifications will occur to a person skilled in the art.

I claim:

1. A machine gun comprising a cradle, a recoiling mass slidingly mounted to said cradle for rearward displacement thereon to a predetermined recoil position responsive to recoil forces produced by discharge of a round in said recoiling mass, energizing means for applying a predetermined force to said recoiling mass for forward displacement thereof from the recoil position, and a firing system comprising a computer, motion measuring sensors disposed for transmitting to said computer for evaluation thereby signals proportional to the forward displacement and the velocity of the recoiling mass and to the acceleration of said cradle, and a comparator, said computer, said sensors and said comparator being operatively disposed in cooperation with each other and together with said energizing means for determining the point of time at which the round is discharged in each firing cycle to neutralize the internal forces created by the firing of the round and to compensate for externally effected disturbances.

2. The invention as defined in claim 1 wherein said sensors comprise a pair of sensors mounted to said cradle to measure respectively the forward displacement and the velocity of said recoiling mass, and an accelerometer mounted to said cradle to measure the acceleration thereof.

3. The invention as defined in claim 2 wherein said cradle includes trunnions for mounting the machine gun to a frame of a transporting vehicle subjectable to conditions adverse to the operation of the machine gun, and wherein said computer, comparator and energizing means are arranged in cooperation to automatically correct for disturbances to the operation of the machine gun resulting from the adverse conditions to maintain the substantially constant recoil force throughout a firing burst.

4. The invention as defined in claim 2 wherein said energizing means comprises a spring disposed between said recoiling mass and said cradle for applying the predetermined force to said recoiling mass for forward acceleration thereof along said cradle, and wherein said computer and comparator cooperate to fire the round during forward displacement of said recoiling mass responsive to signals from said sensors and said accelerometer at a point of time when the recoil force produced by the discharge and reduced by the predetermined force applied thereagainst at the time of discharge is of a value to drive said recoiling mass to the recoil position.

5. The invention as defined in claim 2 wherein the discharge of each round in a firing burst is controlled by the implementation of the equation Q(v,x,i) S(v,P M 2) x in which x and v respectively denote the displacement and velocity of said recoiling mass relative to said cradle, i denotes the acceleration of said cradle, P denotes the predetermined force applied by said spring to said recoiling mass, M, denotes the mass of said recoiling mass and S( v,P) denotes the distance, as a function of velocity, said recoiling mass travels to the rear before coming to rest at the recoil position, whereby the coordinates x and y are measured by said sensors and i by said accelermoter, the measured values are substituted into the equation and evaluated by said computer, and the computed value is monitored by said comparator to signal said firing circuit for firing the round when the computed value goes from positive to negative.

I t I III 

1. A machine gun comprising a cradle, a recoiling mass slidingly mounted to said cradle for rearward displacement thereon to a predetermined recoil position responsive to recoil forces produced by discharge of a round in said recoiling mass, energizing means for applying a predetermined force to said recoiling mass for forward displacement thereof from the recoil position, and a firing system comprising a computer, motion measuring sensors disposed for transmitting to said computer for evaluation thereby signals proportional to the forward displacement and the velocity of the recoiling mass and to the acceleration of said cradle, and a comparator, said computer, said sensors and said comparator being operatively disposed in cooperation with each other and together with said energizing means for determining the point of time at which the round is discharged in each firing cycle to neutralize the internal forces created by the firing of the round and to compensate for externally effected disturbances.
 2. The invention as defined in claim 1 wherein said sensors comprise a pair of sensors mounted to said cradle to measure respectively the forward displacement and the velocity of said recoiling mass, and an accelerometer mounted to said cradle to measure the acceleration thereof.
 3. The invention as defined in claim 2 wherein said cradle includes trunnions for mounting the machine gun to a frame of a transporting vehicle subjectable to conditions adverse to the operation of the machine gun, and wherein said computer, comparator and energizing means are arranged in cooperation to automatically correct for disturbances to the operation of the machine gun resulting from the adverse conditions to maintain the substantially constant recoil force throughout a firing burst.
 4. The invention as defined in claim 2 wherein said energizing means comprises a spring disposed between said recoiling mass and said cradle for applying the predetermined force to said recoiling mass for forward acceleration thereof along said cradle, and wherein said computer and comparator cooperate to fire the round during forward displacement of said recoiling mass responsive to signals from said sensors and said accelerometer at a point of time when the recoil force produced by the discharge and reduced by the predetermined force applied thereagainst at the time of discharge is of a value to drive said recoiling mass to the rEcoil position.
 5. The invention as defined in claim 2 wherein the discharge of each round in a firing burst is controlled by the implementation of the equation Q(v,x,z) S(v,P - Mgz) - x in which x and v respectively denote the displacement and velocity of said recoiling mass relative to said cradle, z denotes the acceleration of said cradle, P denotes the predetermined force applied by said spring to said recoiling mass, Mg denotes the mass of said recoiling mass and S(v,P) denotes the distance, as a function of velocity, said recoiling mass travels to the rear before coming to rest at the recoil position, whereby the coordinates x and y are measured by said sensors and z by said accelermoter, the measured values are substituted into the equation and evaluated by said computer, and the computed value is monitored by said comparator to signal said firing circuit for firing the round when the computed value goes from positive to negative. 